Based on my own experience and research on this subject, I'd like to offer some additional suggestions.
1. Keep a record (spreadsheet) of your blood sugar readings. Have a comments column for any anomalous readings (foods eaten, exercise, sleep quality, stress, illness etc.)
In my spreadsheet, I keep track of daily fasting blood sugar levels (measure right after waking up and before eating/drinking anything. should record the exact time if you don't usually wake up at the same time).
Diabetes Tests and diagnosis - Mayo Clinic
"A fasting blood sugar level less than 100 mg/dl (5.6 mmol/L) is normal. A fasting blood sugar level from 100 to 125 mg/dL (5.6 to 6.9 mmol/L) is considered prediabetes. If it's 126 mg/dL (7 mmol/L) or higher on two separate tests, you have diabetes"
I also record blood sugar levels after 2 hours of eating (counted from the 1st bite) breakfast, lunch and dinner. I only measure this 2-hour level few times a week for a while mainly to figure out what food/drink trigger high blood sugar
Few years ago when I did intensive research on the subject, one doctor's website stated that the postprandial plasma glucose is the most important level and this should be measured 2-hour post meal.
>200 mg/dL: diabetic
>140mg/dL <200 mg/dL: prediabetic
Please note that the readings can vary from brand to brand if the meter/strip is not calibrated. Even when it is calibrated, you can different readings using different strips on the same meter (yes, I have tried to do this and found +- 5 units).
From my experience, there are many factors which can affect blood sugar level (especially the fasting blood sugar values): stress, quality of sleep, illness, medications etc. Few weeks ago, my blood sugar levels went up 20-30 units for a week after my flu shot!
2. Have a column in your blood sugar spreadsheet to record your activity/exercise levels the day before.
After keeping track of your blood sugar levels and daily exercises, you will find that there is a VERY STRONG CORRELATION between the two.
Regarding diet, I strongly agree with the recommendation to add more protein to your diet. I have also read that eating protein rich food at the same time with carb helps to slow down glucose absorption to your blood stream.
I was diagnosed of being marginally diabetic 3 years ago. My doctor told me that I had done everything right (had 'my plate' diet with whole grains, exercised >30 minutes daily, BMI at 18) and attributed the condition to genes.
I did not want to take medications (it's difficult for a diabetic pilot to maintain medical certificate) so I decided to improve my diet and exercise levels.
I modified the 'my plate' diet from 1/4 protein, 1/4 grains, 1/4 fruits, 1/4 vegetables to 1/3 protein, 1/3 vegetables, 1/6 grains and 1/6 fruits. In the summer, I consume more fruits but try to cut back even more in grains level (no white starches, white rice/bread and white potatoes). I should also note that low-fat products are usually loaded with sugar and if anything, fat is good for diabetic person. I drink whole milk, eat lots of cheese and butter. I also eat lots of nuts.
My physician brother recommended doing at least 45 minutes of exercise a day (walking, biking etc.). I also found that a combination of aerobic and strength training worked the best. Tone muscles are much better in burning calories and using blood glucose than flappy ones. I have tried to maintain at least 60 minutes of aerobic exercise a day and 20-30 minutes weight lifting every other day. I highly recommend to use a tracking device like fitbit to keep track of your daily activities. Steps and stair counts are great ways to make sure that you get enough exercises.
By keeping track of my blood sugar levels, changed my diet and upped my daily exercise level, I have managed to get down to pre-diabetic or marginally pre-diabetic in the last 2.5 years. A side benefit is that cutting back on carbs also helps to loose weight. I don't need to loose weight but lost 3 lbs after 3 months (down to 97lbs from 100lbs - 5' 2"). My doctor kind of scolded me for being skinny but my other physician brother told me that my weight was fine for a small frame person. I am quite healthy and very strong for a person of my age and weight level.
Good luck with your efforts.